1. Field of the Invention
The present invention relates to syringes, and more particularly to an improved reusable autoinjector syringe apparatus. Even more particularly, the present invention relates to an improved auto injector syringe apparatus that accepts disposable syringe cartridges containing a drug or medicament to be dispensed, with a cam arrangement that automatically projects the cartridge needle from a retracted to a projected position into the patient, dispenses the drug or medicament, then retracts the needle.
2. General Background of the Invention
Various forms of spring equipped syringe holders and actuators are known in the art such as the ones shown in my prior U.S. Pat. No. 5,267,963. Other spring equipped syringe holders or actuators include for example U.S. Pat. No. 3,941,130 issued to Tibbs; U.S. Pat. No. 4,261,358 issued to Vargas et al; and U.S. Pat. No. 4,188,950 issued to Wardlaw.
In my prior U.S. Pat. No. 5,267,963, there is provided an automatic injection device which, upon activation by the user, automatically extends a syringe with a needle, delivers medication through the needle and then retracts the needle thus keeping it hidden from view. U.S. Pat. No. 5,267,963 is incorporated herein by reference.
In my prior co-pending patent application Ser. No. 08/943,423, there is provided a dual chamber syringe apparatus that enables a user to reconstitute a drug product that includes a dry portion and a liquid diluent portion.
It is known that many drugs cannot be administered by the oral route because of gastrointestinal intolerance, irregularity in absorption, and metabolic breakdown in the gut wall and liver (first pass effects). In particular, first pass loss abolishes oral bioavailability of all poly-peptide and protein medications [e.g. growth hormone, tumor necrosis factor receptor, insulin, alucaaon, alteplase, erythropoietin, alglucerase (glucocerebrosidase-B-glucosidase), etc.]. This necessitates their administration through various parenteral routes, i.e., intravenous, intramuscular, subcutaneous, intrathecal, etc. Further, parenteral delivery of such drugs will expand with future mapping and functional understanding of the human genome. Pharmaceutical recombinant DNA synthesis of new peptide-protein moieties will concomitantly increase, and make a cost-contained, safe, effective and simple to use delivery device essential for both patients and medical professionals.
Functionally, stability of an injectable drug may be defined as its capability to retain chemical, sterile, toxicological and therapeutic specifications within 90% of its original potency. By tradition, expiration dates denote the last day of a month and year a particular preparation retains such stability under recommended conditions. In case of a dry or lyophilized medication to be reconstituted prior to use, expiration dates are designated for both the dry and reconstituted product. When compared to drug solutions ready for injection, dry soluble medications ready to be reconstituted with solvent just prior to use are well known to have greater stability and longer expiration dates.
Time related deterioration in ready to use parenteral drug preparations include interactions between combined active, and between active and inactive ingredients. Aqueous solvents in particular, potentiated by heat and radiation, initiate or accelerate time dependent degradation through oxidation, reduction, hydrolysis, racemization, decarboxylation, photolysis, and, autooxidative free radical chain reactions.
Notwithstanding such chemical breakdown, buffers, antioxidants, preservatives and other stabilizers oftentimes cannot be used in formulations containing water because of their reactivity with the active ingredient(s) or, direct patient hypersensitivity. Moreover, water itself has a profound effect on hydrolysis and denaturation of drugs possessing ester or amide chemical bonds, e.g. tetracaine, physostigmine, growth hormone, benzylpenicillin, calcitonin, epoetin alfa, menotropins, placental gonadotropin, interferons, pituitary releasing hormones (gonadorelin, cosyntropin, etc.) and numerous others.
A cost effective, simple, self contained dual-chamber syringe which isolates dry-wet drug components and mixes them immediately prior to injection is highly desirable. Furthermore, such a device would eliminate extra standard syringes, medication and diluent containers required for mixing the individual drug constituents. The device would permit accurate drug reconstitution, eliminate waste and possible introduction of contaminants through human error.
An automatic injection type syringe that operates with a disposable cartridge should preferably be configured to function with either a dual chamber or single chamber syringe.